◆ Concrete

Round concrete ashtray mold

A heavy round ashtray, 100 mm across with three cigarette rests, to cast in concrete. A silicone mold kit from printed parts.

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3D render of the round concrete ashtray master with three cigarette rests, fused on its printed charcoal base between the orange and blue round walls, with the charcoal clamps behind
Concrete ~294 g Pro early access

A round concrete ashtray 100 mm across and 34 mm tall: a chunky ring that leans in slightly toward a rounded rim, a bowl 68 mm across and 22 mm deep over a 12 mm floor, and three U-shaped cigarette rests across the rim that tip toward the bowl, so ash falls in. At about 463 g in concrete it will not tip or blow off a balcony table.

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Made with the box mode of our silicone mold maker in its round shape, the mode both the site's mold advisor and the tool itself suggest: the bowl would lock any rigid two-part mold. Print the base with the ashtray fused onto it, the two walls and the two clamps, and pour about 508 ml of silicone. It fills the bowl and becomes a core, and because the ashtray is widest at its foot, each cast slides out of the block with no cut.

Cast it in fine concrete or Jesmonite, never resin: resin scorches under a cigarette. Seal it so ash and tar wipe off, or use it as an incense ash catcher, a palo santo dish, a key bowl or a jewellery dish. The zip carries every printed part, the ashtray master as its own STL, the tool's own print-settings sheet and a recipe file for the generator.

Shown as a 3D render of the printed mold parts pulled apart around the master, not a photo.

What you need

4
  • About 549 ml of silicone (mix it in one batch)
  • Fine concrete or Jesmonite (not resin or plaster for cigarettes): each ashtray is 210 ml, about 463 g in concrete
  • Tape for the wall seams
  • Fine sandpaper, a penetrating concrete sealer and felt pads

How to cast it

8

  1. Print the base with the master fused onto it, the two walls and the two clamps.

  2. Stand the base on the table. Set each wall down a few centimetres out from it and slide it in over the table until the ridge round the base sits in the groove at its foot, then slide the clamps down over the seams. Once they are on, the walls cannot lift, and the ridge seals the bottom.

  3. Mix 549 ml of silicone in one batch and pour it in a thin stream down the inside of a wall, letting it rise round the master and into its well until it covers the top.

  4. Once it has cured, take the clamps off, slide the walls straight out and pull the silicone block off the master. That block is your mold.

  5. Turn the block over and stand it back inside the walls with the clamps on. The opening is the foot of the ashtray, with the silicone core standing up in the middle.

  6. Mix a fine concrete or Jesmonite a little wetter than for a slab, pour it slowly down one side of the ring round the core, and tap the walls for a minute to raise the air. Fill level with the opening and strike it flat.

  7. Leave it to cure for a day, take the walls off, peel the silicone off the outside and twist the ashtray off the core. Sand the foot flat and seal it.

  8. Let it dry for a few days, then brush two coats of a water-based penetrating concrete sealer over the bowl and the rests, so ash and tar rinse off instead of staining.

Print details

8 h 50 minPrint time
~294 gFilament
5Printed parts
128 × 128 × 72 mmSize (W x D x H)
All print details
Print details
Cast materialConcrete
Printed parts5
Size (W x D x H)128 x 128 x 72 mm
Print bed needed150 x 128 mm, 72 mm tall
Filament~294 g
Layer height0.2 mm
Infill15%
SupportsNot needed
DownloadZIP: 5 printed parts (STL) + ashtray master (STL) + print sheet + recipe
Added2026-09-26

Pro early access until October 26, 2026, then free with any account.

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Made with the free Silicone mold maker generator. Upload your own model and get the same kind of mold built around it, in your browser.

Free for personal use. Selling the pieces you cast needs a commercial licence (Pro or Founder); passing on the file itself is not permitted on any plan. Full terms.

New to casting? Read the silicone mold maker guide.

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Questions about this design

Is a concrete ashtray from the round ashtray mold safe with lit cigarettes?

Yes. Concrete and Jesmonite do not burn, and the 12 mm floor keeps the heat off the table. Do not cast this ashtray in resin or plaster for use with cigarettes: resin scorches and gives off fumes, and plaster soaks up tar and cracks with heat. Stand it on a hard surface outdoors or near an open window.

How do I seal the round concrete ashtray so it stays clean?

Let it dry for a few days, then brush on two coats of a water-based penetrating concrete sealer, inside the bowl too. Sealed concrete keeps ash and tar on the surface, so it rinses clean under the tap with a soft brush instead of staining grey-brown.

Why does the round concrete ashtray come out of the silicone without a cut?

Because its side leans in 3 degrees from the 100 mm foot to the rim, so nothing above the foot is wider than the opening it leaves through. The silicone core that forms the bowl is widest at the rim too, so the cast twists off it cleanly, with the rests formed by small silicone tabs.

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